The present invention disclosed herein relates to a semiconductor device and method of forming the same, and more particularly, to a NAND-type nonvolatile memory device and method of forming the same.
Nonvolatile memory devices have the property that stored data is maintained even when an external power supply is stopped. A representative of the non-volatile memory devices is a flash memory device that can electrically write and erase data. The flash memory devices can be classified into NOR-type flash memory devices and NAND-type flash memory devices. The NOR-type flash memory devices are widely used in apparatuses requiring a high speed operation because they enables a high speed random access. The NAND-type flash memory devices are widely used as a large capacity storage unit because they have excellent program and erase speed and can easily attain high integration.
As semiconductor devices tend toward high integration, semiconductor manufacturing processes reach limits in reducing a plane area of unit cells of the NAND-type nonvolatile memory device. For example, a photolithography process for defining a line width of a gate included in a unit cell reaches a limit. Also, the semiconductor manufacturing processes reach a limit in securing characteristics necessary for the unit cell according to the reduction in the line width of gate. On the other hand, as semiconductor industries are highly developed, higher capacity NAND-type flash memories are required. In recent years, NAND-type flash memory devices capable of storing tera (T) bits data are required. Accordingly, many researches on methods capable of further increasing the integration density of the NAND-type flash memory devices have been conducted.